I. Field of the Invention
The field of the invention is hand-held graphical computers which assist human decision-making in monitoring and controlling industrial processes.
II. Description of the Prior Art
In monitoring and controlling nuclear plant operations instruments are used to measure various parameters in the reactor vessel, its supporting subsystems and the surrounding containment vessel. When conditions are sensed that are outside the normal operating range of various parameters, there is a need for human decision-making. One approach to assisting operating personnel has been to provide a book of charts showing various sets of conditions for multiple parameters. The possible conditions of each parameter are related in a network so that each condition for a selected parameter is located on a different path from the other condition for that same parameter. Each path also contained a set of conditions for multiple parameters that were related to a result or action to be taken and this was located at the end of each particular path. This network resembled a decision tree of the type disclosed in Magee, "Decision Trees for Decision Making", Harvard Business Review, July-August, 1964. A technical problem with these networks was that the operators had to trace the correct path while keeping in mind the conditions applicable to several parameters.
One approach to improving aids available to operators was the provision of a computer program which analyzed parameter conditions that were entered through a CRT terminal. The terminal displayed these events in a network along with a resulting decision or direction to employ a specific operating procedure.
This approach was relatively expensive, it required some knowledge of computer operations, and the computer equipment lacked portability. There was therefore a need for a low cost, simple and inexpensive hand-held computer to be carried by the operators.
Mechanical computers have usually been of the counting or slide rule type in which a scale placed on one member and a pointer on the other member is moved relative to this scale to select different values for a particular parameter. The value of this parameter therefore depends upon the distance moved by the pointer
For example, Bean, Jr., U.S. Pat. No. 3,034,708, issued May 15, 1962, shows a five-layer graphical computer for use in actuarial, insurance and pension matters. As seen in FIG. 4 of Bean, this computer has top and bottom stationary layers 1 and 2, movable slide members 5 and 6, and a middle transparent stationary sheet 3. The top cover 1 and the upper slide 5 have apertures for viewing indicia on the lower members. The apertures 8, 9 and 11 in sheet 3, slide 6 and bottom cover 2 relate to the manner of sliding movable slide members 5 and 6.
The basic method of calculating is performed when pointers 20 and 21 in FIG. 3 of Bean are moved relative to scale 19 on the middle transparent layer to indicate two inputs, which are retirement age and present age. Pointers 20 and 21 are carried by the movable members 5 and 6, which also carry a window and a scale, respectively, to produce an output, which is months to retirement. One output is calculated according to the following equation: EQU (Retirement Age-Present Age).times.12=Months to Retirement.
In Bean, Jr., the position of a pointer along one scale determines the position of an index window along another scale. By moving both the index window and the second scale, a subtraction can be accomplished. The multiplication can be predetermined and reflected in the units selected for the result.
Sellie, U.S. Pat. No. 3,650,467, shows a time-motion calculator with windows in the top sheet of an envelope. Next to these windows are parameter values. When the operator positions the parameter indicator on the movable sheet beneath the parameter window next to a value, a corresponding set of results appears through a result window. The results are carried on the same card as the parameter pointer. In this device there is a one-to-one correspondence between each input and each output. There is no calculation or mathematical operation carried out by the computer. The mathematical operations have been predetermined and included in the result numbers.